Connecting 3 racks

We are doing a FOH, Monitor, Broadcast setup each with its own DM or CDM. I realize each DM needs an additional gigs ace card in order to share information. My setup will be as follows

CDM 1 (FOH)
Giga ace card (interconnects DM2)

DM2 (MONITORS)
GIGA ACE 1 (interconnects CDM1)
GIGA ACE 2 (interconnects DM3)

DM3 (BROADCAST)
GIGA ACE (interconnects DM2)

Will I be able to tie line from CDM1 to an output on DM3? Send stems from FOH to broadcast?

yes, it will be possible
but you have to do some routing on all three systems

otherwise it is possible to link them with Dante, then you can route in Dante independent from the consoles